Meghan Hodges
Thermal pollution, also known as thermal enrichment, is the degradation of water quality due to changes in the ambient temperature of a natural body of water. This can be caused by both human and natural factors. One significant human source of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. Water is used to cool machinery, absorbing heat in the process, and is then returned to its source at a higher temperature. This sudden change in temperature can decrease the oxygen supply, increase the metabolic rate of aquatic animals, and compromise the biodiversity of the ecosystem.
| Characteristics | Values |
|---|---|
| Definition | Degradation of water quality by any process that changes ambient water temperature |
| Other Names | Thermal enrichment |
| Causes | Use of water as a coolant by power plants and industrial manufacturers, urban runoff, soil erosion, natural causes (e.g. volcanoes, wildfires, geothermal vents), lightning, climate change |
| Effects | Decreased dissolved oxygen levels, increased metabolic rate of aquatic animals, harm to water-dwelling plants and animals, altered oxygen levels, increased vulnerability to chemicals, decreased biodiversity |
| Solutions | Converting to closed-loop systems, banning wastewater dumping, offering incentives for eliminating once-through cooling systems, switching to clean energy |
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What You'll Learn
Industrial processes and facilities
Thermal pollution is a growing concern, especially with climate change exacerbating increases in water temperature. It is caused by a rise or drop in the temperature of a natural body of water due to human activities, which degrades water quality and harms aquatic life. One significant source of thermal pollution is industrial processes and facilities, which often use large amounts of water from natural sources and discharge heated wastewater back into the environment.
Industrial facilities, such as factories, manufacturing units, and power plants, often use water for cooling machinery, which then becomes very hot. This heated water is subsequently released back into natural water sources, causing a sudden increase in water temperature. This temperature rise can have detrimental effects on aquatic ecosystems, including reduced oxygen levels, altered metabolic rates, and decreased biodiversity.
Power plants, in particular, contribute significantly to thermal pollution. Thermoelectric power plants fuelled by coal, natural gas, nuclear energy, or biomass use water for cooling and convert it to steam to drive turbines for electricity generation. The water used for cooling absorbs heat, and if discharged back into rivers, lakes, or oceans, it raises the temperature of these water bodies. This was the case with the Potrero Generating Station in San Francisco, which used once-through cooling and discharged water approximately 10 °C above the ambient bay temperature.
In addition to power plants, other industrial facilities contribute to thermal pollution. These include petroleum refineries, pulp and paper mills, chemical plants, and steel mills. These industries release large amounts of effluents and coolant water, which can lead to a sudden drop in dissolved oxygen levels, causing the death of aquatic animals. The sugar manufacturing units, paper and pulp industry, and textile units are significant contributors to this issue.
To mitigate thermal pollution from industrial processes and facilities, several measures can be implemented. Converting facilities from once-through cooling to closed-loop systems can help reduce temperature changes. Implementing cooling ponds, cooling towers, or cogeneration systems can also control water temperatures before release. Additionally, reducing water discharge, capturing and reusing heated wastewater, and improving water treatment processes can help minimize thermal pollution from industrial sources.
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Natural phenomena
Wildfires today are more frequent and severe due to human-induced climate change and forest mismanagement. Climate change can also lead to cold-water thermal pollution because it causes glaciers to melt faster.
Deforestation removes the shade that trees and plants provide for water bodies, resulting in increased sunlight exposure and higher water temperatures. Soil erosion near rivers and streams causes their beds to become wider and shallower, exposing more areas to sunlight and heating the water.
In urban areas, rainwater can flood retention ponds, which are wide and shallow and thus heat up quickly in the sun. If the water spills out, it can run off into nearby natural bodies of water, increasing their temperature.
While natural phenomena can contribute to thermal pollution, human activities, particularly industrial cooling and power generation, are the primary drivers of this form of pollution.
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Soil erosion
Human activities that contribute to soil erosion include deforestation, the conversion of natural ecosystems to pasture land, and crop production. Deforestation removes trees that usually prevent sunlight from falling directly on lakes, ponds, or rivers. With the trees and vegetation cover removed, bodies of water are exposed to more sunlight, causing them to heat up. This phenomenon is known as thermal pollution, which is caused by the sudden increase or decrease in the temperature of a natural body of water.
Additionally, the conversion of natural ecosystems to pasture land can lead to high rates of erosion, loss of topsoil, and nutrient depletion. Overgrazing can reduce ground cover, making the land more susceptible to erosion and compaction by wind and rain. This harms soil microbes and reduces the ability of plants to grow and water to penetrate the soil.
Crop production can also increase soil erosion beyond the soil's ability to maintain itself. Certain crops, such as coffee, cotton, palm oil, soybean, and wheat, have been found to contribute to significant soil erosion. Pesticides and chemicals used in crop production can alter soil composition and disrupt the balance of microorganisms, favouring the growth of harmful bacteria.
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Runoff from paved surfaces
Thermal pollution, also known as thermal enrichment, is the degradation of water quality by any process that alters the ambient water temperature. This can be caused by human activities or natural phenomena. Runoff from paved surfaces is a significant contributor to thermal pollution, particularly during the summer months when temperatures are at their peak.
During hot weather, rainwater that falls on paved surfaces such as roads, parking lots, rooftops, and sidewalks can absorb heat and contribute to thermal pollution when it enters nearby water bodies. This is especially true in urban areas with a high percentage of impervious, paved surfaces. The impact of runoff from paved surfaces on water temperature has been the focus of many studies in recent years due to its potential harm to aquatic life.
One study from Minnesota found that an asphalt parking lot contributed to increased stream temperatures during large rainfall events. Similarly, another study found that rainwater runoff from asphalt pavement in urban roads increased the temperature of receiving water bodies by 5°C, and even up to 10-12°C under extreme conditions. These temperature changes can have detrimental effects on aquatic organisms, as elevated temperatures decrease the level of dissolved oxygen in the water, which is essential for the survival of fish and other aquatic life.
The impact of runoff from paved surfaces on thermal pollution can be mitigated through the use of reflective and permeable pavements. Stormwater management facilities, such as bioretention systems and infiltration basins, can also help reduce thermal pollution by allowing water time to release excess heat before entering natural water bodies.
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Power plants
Thermoelectric power plants, including those fuelled by coal, natural gas, nuclear energy, biomass, and other waste products, are major contributors to thermal pollution. For example, a 2016 global analysis of thermal pollution in rivers found that the Mississippi River had the highest heat emissions, with 62% coming from coal-fired power plants and 28% from nuclear power generation. Similarly, a study of 128 power plants along the Mississippi River Watershed showed that thermal pollution from upstream plants impaired the energy efficiency of downstream plants, as they used the warmed water for their cooling processes.
Nuclear power plants, in particular, have been associated with thermal water pollution. While nuclear power is often touted as a more environmentally friendly alternative to fossil fuels due to the absence of direct greenhouse gas emissions, it still contributes to thermal pollution. Nuclear power plants use water in various stages of the power generation process, including process water and cooling water. The heated water released from these plants can have detrimental effects on aquatic life, accelerating the metabolism of cold-blooded animals, leading to malnutrition and changes in biodiversity.
To address thermal pollution from power plants, several strategies can be employed. One approach is to implement effluent treatment processes, carefully store wastewater in ponds, or reinject it into deep wells. Additionally, reducing the amount of water released by power plants and capturing heated wastewater for other purposes, such as desalination, can help mitigate thermal pollution. Governments can play a role by offering incentives for companies that eliminate once-through cooling systems and enforcing regulations like the federal Clean Water Act in the US, which sets limits on thermal discharges to protect aquatic life.
It is important to note that the impact of thermal pollution from power plants extends beyond the immediate vicinity of the plant. Downstream communities may bear the brunt of the pollution, even though they are not directly responsible for its creation. As such, addressing this issue requires a comprehensive approach that considers the broader chain reactions and seeks to balance power generation with the preservation of our vital natural water resources.
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Frequently asked questions
Thermal water pollution is the degradation of water quality by any process that changes the ambient water temperature.
One source of thermal water pollution is the use of water as a coolant by power plants and industrial manufacturers.
Power plants and industrial manufacturers use water to cool machinery, which then heats the water and sends it back to the natural source at an elevated temperature.
Thermal water pollution can harm aquatic life by decreasing oxygen supply and altering the composition of ecosystems.
